Irrigation headaches

By Phil Jeselnik, American Society of Landscape Architects

Of the problems that can occur in an irrigation system, those
associated with sprinkler heads are the most noticeable to clients
and the public. These problems are visually noticeable and manifest
themselves in non-uniform green areas of the turf (donut patterns
and dry spots), ponding water and misting and drifting that cause
wet sidewalks and streets.

If these conditions exist on a landscape that you manage, the
first thing you should do is evaluate your sprinkler heads. To do
this, you need to figure out what type of sprinkler head your
irrigation system uses. Most modern sprinkler systems include two
types of heads: spray and rotary. The type of head used by your
irrigation system depends on the dimensions of the area it is
irrigating, water pressure available for operation and a variety of
other factors.

Spray heads

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Spray heads are what people commonly think of when they think of
irrigation heads. These types of heads are uniformly spaced within
an area and are used to irrigate lawns, shrubs and groundcover
beds. The main difference between spray heads and other types of
heads is their spacing. Although the spacing of spray heads can
vary depending upon the specific nozzle the designer selected to
use in the head, they are usually not spaced more than 15 feet
apart. The majority of spray heads are “pop-ups,” which
are designed with the nozzle on the tip of a riser that can pop up
2 to 12 inches out of its housing during operation. When irrigation
is complete, water pressure drops and the riser retracts to the
soil line so that it is out of sight and does not interfere with
mowing or normal use of the lawn. The 6- and 12-inch pop-ups are
called “high pop-ups” and are used in shrub and
groundcover beds as well as flowerbeds. You can also install spray
heads in planting beds on fixed risers that do not pop up. You
should base riser height on the projected height of the shrubs and
plants to provide uniform application of water.

Rotary heads

Rotary heads are larger than spray heads and are usually used to
irrigate larger areas including commercial property, parks, large
lawns and sports fields. They can project water a distance of 20 to
50 feet or more. Like spray heads, rotary heads are available as
pop-ups or fixed versions on risers. There are two types of rotary
sprinklers: gear-driven and impact. The difference between them
lies in the mechanism that causes them to rotate.

Impact rotors. Impact heads were originally developed
for watering agricultural crops in the 1930s and have been used in
landscape irrigation since the 1940s. A spring-loaded arm causes
impact heads to rotate. As water flows from the outlet in the head,
it triggers the arm to pivot away from the water stream until it
hits a stopper attached to the head assembly. The spring causes
tension in the arm, which then returns the arm to its original
position, and the process starts again. The impact against the
stopper causes the entire assembly, including the stream of water,
to rotate slowly. The slow, continuous rotation of the assembly
will slowly irrigate its designated area.

You can set up impact heads to irrigate in a full or part
circle, depending on your needs. Just switch the lip or spring to
reverse the rotation and cause the assembly to move backwards
before it completes a full circle of revolution. This
back-and-forth rotation allows you to get better use of a sprinkler
in areas such as corners and along curbs and walks.

The coverage provided by impact-type rotors can be highly
uniform. However, they also can be high maintenance. When you
activate an impact sprinkler, it rises out of the head casing,
exposing the open housing of the head. This open cavity is prone to
catching mud, grass clippings and other debris. Therefore, it
requires frequent maintenance to keep the housing and mechanisms
clean, which is especially important in preventing damage to the
assembly. Impact rotors also have many exposed, moving parts. The
springs can be especially troublesome because clippings and twigs
can become entangled in them. They are also easily bent, can fall
off the assembly and are prone to rust. Another negative
characteristic is their clatter during operation, which can be
annoying to some people.

Gear-driven rotors: Gear-driven rotary sprinklers are
used in most modern systems and are the most popular type of rotary
head. Water turns a small turbine in the base of the unit, which
drives a series of gears that cause the head to rotate. Unlike
impact sprinklers, the drive mechanism is sealed from dirt and
debris, quiet during operation and easy to adjust. However, because
of their long throw of water, it's easy for inexperienced designers
to misuse and misapply them. Although gear rotors cost more than
spray heads, their wider spacing capability means that you'll need
fewer heads to cover a given area. Consequently, landscapers
frequently use them in spaces too small for efficient rotor
operation in an attempt to reduce the number of heads, connections,
trenching and labor costs. If you force a rotary sprinkler to cover
an area too small for its intended design, you will get increased
misting and inefficient coverage, especially if you have to adjust
it below the manufacturer's specification.

Sprinkler nozzles

Nozzles are the devices that disperse water onto the landscape
as it passes through the head assembly. They control the amount of
water being applied and the distance of throw. The amount of water
distributed over an area can vary greatly depending on the nozzle
selected.

Assessing spray-head and rotor performance

Problems with spray heads and rotors can be caused by major
system flaws resulting from poor overall design including improper
zone layout, lack of proper overlap and disregard for available
pressure and flow. It is more than likely, however, that the
problems are non-system related. Fortunately, non-system-related
problems are easier and less expensive to correct.

Non-system related problems that affect head performance
include:

Heads that are too close to walks and pavements

Displaced heads that are sunken, offset or unstable in the
soil

Improper installation and repairs (including keeping dirt and
debris out of the system)

Normal head wear and tear

Incorrect arc adjustment

Obstructions such as turf and branches

Water quality including secondary water, well water and surface
water from a pond or stream

Broken heads as a result of lawn mowing, edging or snowplowing,
or from the roots of a growing and maturing tree or shrub.

Donut patterns and other dry spots could be the result
of a number of problems associated with heads, including
non-compatible heads in the same zone, lack of proper overlap,
basic nozzle or arc adjustment and obstructions caused by turf,
plants or structures.

Misting and drift is caused by high pressure at the
sprinkler nozzle that results in the breakup of spray into a fine,
atomized mist that sometimes looks like fog. The presence of
misting is an indication that you should make adjustments to
increase the size of droplets by either regulating pressure or
changing the type of head or nozzle.

Spitting, lack of discharge and general poor head
performance is probably an indication of clogged nozzles or
partially closed valves resulting from low pressure. Debris in the
nozzle can misdirect the spray and result in partial spray patterns
or even a complete plugging. You should carefully remove debris in
nozzles. Digging or gouging could permanently change the spray
pattern. Clean nozzles with air, water or a soft-bristled brush,
such as a pipe cleaner. Using a wire or a screwdriver can
permanently scratch the nozzle and misshape the orifices.

Rotation flaws are likely an indication of:

Debris in the sprinkler head

Pressure that is too low or high

Flow that is too low

A damaged head

Normal wear and tear

Oversized nozzles

Improperly adjusted flow-control valve

Vegetation obstructions

A bypass in need of adjustment

Foreign lubricants.

Excessively rapid rotation of rotary heads is likely an
indication that the pressure is too high and you need to regulate
it.

Damaged heads could be the result of vandalism, poor
head location, pressure problems, normal wear and tear or poor
maintenance procedures.

Runoff, ponding and soggy turf could be signs of major
problems unrelated to the system or heads. There are a number of
reasons these conditions exist including grading problems,
compacted soils, an improper watering schedule, system drainage to
a low head or valve problems. However, if the problem is
associated with spray heads and rotors, these could be the
causes:

Improper head layout and location

Head rotation problems

Leaking or stuck sprinkler

Improperly adjusted arc

Cracked housing

Non-compatible heads in the same zone.

Common irrigation mistakes that affect sprinkler heads

The following is a list of the most common irrigation mistakes
that pertain to using and maintaining spray heads and rotors.
Correcting them is generally simple and inexpensive and could
reduce your operating costs.

Adjusting or reducing the throwing distance of nozzles more
than 25 percent of the manufacturer's specifications. Besides
violating the manufacturer's specifications and warranty, this
adjustment will produce an uneven precipitation, wasting water and
increasing operation costs.

Disregarding significant overspray. Overspray wastes
water, is irritating and leaves a negative impression with the
public. Liability is also an issue with overspray because it can be
potentially hazardous to pedestrians and motorists and can
deteriorate pavements, curbs and other structures.

Exceeding the manufacturer's specified head-to-head
spacing. Space heads at a distance equal to the selected
nozzle's throwing distance at working pressure as listed in the
manufacturer's catalog. In the end, using a greater distance
between heads will cost clients more in operating costs than can be
saved during installation.

Installing different types of irrigation heads on the same
zone. The precipitation rate for different types of components
varies greatly. If you install heads with a lower precipitation
rate in a zone with heads that have a higher rate, they will not
apply water uniformly and dry spots will occur. Also, you will have
to run sprinklers in these zones longer in order to apply enough
water to irrigate the dry spots. This will result in wasted water,
higher water and energy bills for the client and increased wear on
the system — all without necessarily correcting the
non-uniform appearance of the lawn.

Installing heads on risers next to pedestrian areas.
Heads on fixed risers next to sidewalks, plazas and play areas can
be a danger. A person or pet could fall on one of these hazards,
causing injury or death. If you routinely incorporate these in your
systems, you should notify your insurance agent to make sure you
have sufficient liability coverage to protect yourself and business
should an accident occur.

Using incorrect nozzle patterns for the area you are
watering. Irrigation manufacturers make their spray nozzles in
several part-circle patterns that throw water a maximum distance
ranging from 8 to 15 feet. A professional irrigation designer will
only use nozzles that have the correct pattern and distance
required for an area. Using the incorrect pattern and throwing
distance will, over time, waste a considerable amount of water and
significantly increase operating costs.

Using nozzles within zones that have mismatched
precipitation rates. Many landscapers assume that, in order to
water an area evenly with rotor heads, they need to use the same
GPM nozzles in every head. However, manufacturers make different
GPM nozzles resulting in more flexibility for you. Save water used
in a zone by proportionally matching the precipitation rate of the
nozzles.

Make sure you've got it covered

As professionals, you know that maintaining a system for uniform
coverage in the most efficient and cost-effective manner requires a
broader knowledge of system pieces and parts than just the heads.
It also requires skilled knowledge in the art, science, engineering
and management of irrigation components in general. You cannot
assess major system or zonal problems without looking at the system
as a whole. You can quickly tell if a system is professionally
designed, installed and maintained or if the work is a result of
inexperience or indifference. The performance of a system depends
on the integrity of its design, installation and maintenance. When
any of these three components is compromised, so is the performance
of the system and overall system durability.

Phil Jeselnik is a senior staff designer and project manager for
Jeffrey L. Bruce & Company, L.L.C. (Kansas City, Mo.), which
specializes in landscape architecture and irrigation system design.
You can e-mail him at pjeselnik@jlbruce.com.